This invention relates to a method of producing modified fluff pulp comprising treating cellulose pulp with a nitroxide-mediated oxidation method and fluffing the treated cellulose pulp. The invention further relates to the modified fluff pulp prepared therefrom and absorbent articles comprising the modified fluff pulp.
Cellulose products such as absorbent pads and other structures are composed of fluffed cellulose fibers, which, in turn, are primarily composed of individual cellulose chains. Commonly, cellulose fibers are crosslinked to impart advantageous properties such as increased absorbent capacity, bulk, and resilience to products containing such crosslinked fibers.
Crosslinked cellulose fibers and methods for their preparation are widely known. See, for example, Tersoro and Willard, Cellulose and Cellulose Derivatives, Bikales and Segal, eds., Part V, Wiley-lnterscience, New York, (1971), pp. 835-875. Crosslinked cellulose fibers are prepared by treating fibers with a crosslinking agent. Crosslinking agents are generally bifunctional compounds that, in the context of cellulose crosslinking, covalently couple a hydroxyl group of one cellulose chain to another hydroxyl group on a neighboring cellulose chain. Despite washing the fiber after the crosslinking process, residual amounts of these often expensive crosslinking agents remain in the fiber. Crosslinking agents are known to irritate the skin and require extra production steps in order to remove and dispose of the offending chemicals, particularly in applications where articles composed of these fibers are used directly on the skin. Such processes are often complex and not commercially viable.
However, in general, absorbent articles comprising fluffed crosslinked fibers have greater absorbent capacity, bulk, and resilience than fluffed noncrosslinked or untreated cellulose fibers. Additionally, excessive crosslinking can produce brittle fibers of excessive stiffness, thereby making them difficult to form into densified sheets for transport and to subsequently fluff without fiber damage. Further, when compressed in a dry state, these fibers generally exhibit low responsiveness to wetting. That is, once compressed in a dry state, pads of conventionally crosslinked fluff pulp do not regain substantial amounts of their prior absorbent capacity upon wetting, and may lose their ability to xe2x80x9cwickxe2x80x9d as defined by the ability to rapidly transfer fluid away from the point of insult.
Conversely, absorbent articles, such as pads made from unmodified cellulose fibers, are often excessively flexible, and may lose their structural integrity in the wet state by collapsing. While suitable for some applications requiring a higher density pad, such absorbent articles have low resilience and are characterized by lower overall absorbent properties, particularly under high moisture conditions.
Further, such articles are often unable to maintain their xe2x80x9cwickingxe2x80x9d ability when moistened, as the pad collapses and separates when compressed, thus interfering with the ability of the pad to transfer moisture. The inability to maintain wicking tends to negatively impact the fluid storage capacity of the absorbent article, leads to leaking of the liquid from the article and subsequent irritation of the wearer""s skin. Attempts to increase the absorption of such articles by the incorporation of superabsorbent polymers (particularly hydrogel-forming polymeric materials) may also have an adverse effect on wicking at certain concentrations. This is due to a phenomenon known as xe2x80x9cgel-blockingxe2x80x9d where the expanding superabsorbent polymer gel blocks the open pores within the article and prevents the transfer of fluid to the outer parts of the article.
Attempts to improve the fluid transport properties of absorbent articles have been reported in the literature. Fluid transport properties are defined to be the amount of fluid that can be wicked or transported throughout an article and may be measured by a combination of wicking rate and wicking capacity. Attempts to improve fluid transport properties include the densification of the absorbent article or the addition of high surface area fibers or particles to the article with the intent of increasing the wicking rate. Although these methods effectively create smaller pore sizes in the absorbent article thereby improving wicking rate, they also tend to reduce the wicking capacity of the article having an undesirable impact on the overall fluid transport properties.
Accordingly, there remains a need for a facile process of producing a modified fluffed cellulose pulp having improved absorption properties including absorption capacity, structural integrity, wicking rate and wicking capacity that may be used in absorbent articles.